1. Field of the Invention
This invention relates to a sheet or membrane switch, hereinafter referred to as a "sheet switch", and more particularly, to such a sheet switch which can be advantageously used as a N-key roll-over switch matrix for constituting, for example, a key board switch.
2. Description of the Related Art
Recently sheet switches are widely used as an input means for various apparatuses, as such a sheet switch has a relatively simple construction and is less expensive. Nevertheless due to a requirement for a high speed input, a plurality of keys (N-keys) are sometimes depressed simultaneously and this causes a "bypass signal flow". Accordingly, an appropriate means of effectively preventing or detecting such a bypass signal flow is urgently required.
A known N-key roll-over switch matrix comprises a plurality of X-lines connected to a detection circuit, and a plurality of Y-lines connected to a drive circuit, as shown in FIG. 8. The respective X-lines and Y-lines are connected by a plurality of switch elements and diodes, and each of the switch elements has one end connected to the X-line and the other end connected to the diode connected to the Y-line. The diodes serve to prevent a "bypass signal flow" from the drive circuit to the detection circuit, but such a switch matrix is not suitable for use as a sheet switch, since a plurality of diodes are included therein.
An N-key roll-over type switch matrix which uses a plurality of resistance in place of diodes, as shown in FIG. 9, is also known, but such a known matrix switch usually includes a circuit board on which electrodes, conductive patterns, and resistances are formed.